Electrical ignition system



May 17, 1949. F. R. F; RAMSAY ELECTRICAL IGNITION SYSTEM Filed Feb. 17, 1947 Inventor mond Faber Ra msa Frank Rd) M5 WW4 A ltqrney Patented May 17, 1949 UN IEI ED STATE PAT-9E OEFILCE 2,470,413 ELEGTRICAL IGNITION v SYSTEM Frank Raymond Faber R assignor to -D." 'Napier England, a company Application amsay;Londong Englandf- & son Limited, Ldndon z l v f Great'Britain February 17, 1947',"Se'rial'N0'. 725L089 In :Great Britain February 20,1946 14 Claims. (01. 3151-+209)-* bustion turbines, jetpropulsion apparatus, liquid fuel furnaces, or, the like.

For the sake of conveniencethe termsparking 1 plug!- will be used for thesmember. carrying the sparkTgap. across which'the ignition spark-discharge; takesplace, the term ignition coil will be used totmeana coil of the type normally employed for-coil ignition. in internal combustion engines and having its primary winding associated with the usual contactlbreakers for producing and tim-i inguthe' current vimpulses, and the term magneto will'be used in its usual sense to mean an electrical impulse generator of' the usual character employed to. produce. high tension ignition 'impulses for ignition in an internal combustion engine. Thesterm low-pass impedance willibe used to designate a coil or winding which offers subs'tantialimpedahce to high. frequency currents whilei permitting passage of. low frequency currentsl- Whileathev. above terms willJbe' used with the. meanings referred to,.iteis.to be understood thatthsrelative values of, the primary and 'sec-.

onda'ry windings .ofan ignition coil or a magneto and the usual condenserassociated therewith may forthe purpose of-tthnpresent invention difier from those commonlyjin use at present in accordance with'the requirements. of the present invention.

Irillele'ctrical ignition systemsof the. kind referred to for. internal combustion engines, where l the usual ignitioncoil or magneto is provided with'its secondary winding connected to the sparking ,plug,or.,.p11 S., each sparkloccurs in two phases. breakra high'voltage isbuilt up until it i-onises and breaks down the spark gap,pwhereupon the Firstjonopening of they contact.

capacity,immediatelyassociated .with the gap is discharged as a spark across. the gap. Thi'scapacity is usually very smalLIbing generallylonly the capacityfiof. the hightension lead to" earth,";and

moreover the resistance'of the now ionised gap is small; so, that this initial; discharge is v very brief. The qinitialidischargeg thus produced is followed immediateiwby the second stage" which "consists of a considerablyilonger discharge at lower voltage acrossthe ionis'ed gapg'ofthe energy stored in thlvsecondarywindin'g pf' thetcoil or magneto;

which," being of high"resistance, limits both" the" discharge" -is --'-of the order of-' one-tenth of -an ampere andia'sts for aboutone-thousand micro= seconds.*

It "is found' that sparkingwith this system will fail if the-gap becomes shunted by a=leak-age'" -path,'-"1n"'the form for 'exampleofa conductinglayer'on-the insulator ortheplug; :cf the order of to 1 m'egohm *depending upon-the energyavailable, due to the leakage of theenergyby way of theshuntdeakage pat-h; To overcomethis difficulty a Thigh frequency ignitionsystem has been proposed in-which essentially the-high tension current: impulses from the secondary 5 winding of an ignitioncoil or magneto are" de livered through a spark'gap tothe-primary-winw 'ing of a high frequency transformer :(sometimes known-as a Tesla coil) the secondary'winding ofwhich is connected to the sparking plug or plugs which thus receive high frequency impulses. It has been found that such; highfre'quency impulses will 'bedischarged across the spark gap in prefer ence to passing throughany normally' encoime. tered shunting leakage pathtso, that sparking is assured under-more adversenconditions than .was possible with the old arrangement.

With this so-called \ihigh frequency system, however, while satisfactory operation can "be; obtained, when theengine is"hot, 'it;is. found that starting becomes diflicult. or impossible in ,a cold enginelorflwithllow gradefuels since a greater degree. of local heating than islgiv'en by thehigh frequencylisparkisrequired to ignite the. fuel, WhiIeZ-the system is-Ialso uselessLin otherv cases where thezspark'hasvtoeffect a substantialdegree' of local heating ,of the.fuel tube ignitedvbefore' its actual ignition,;as for example;.infurnace or other. ignitors for comparativelyfheavy fuelsi Arisobject, of the present invention is to..pr0-- vide' animproved ignition system or apparatus" having advantages over the above previous. pro 'posals;

To this end an electrical ignitionsystemac cording, to the s present" invention includes a high frequency circuit i to, be: coupled or connected to a sparking p111g,1means including a trigger spark in the high frequency circuit to initiate high frequency current and ionise the sparking plug gap, and means for supplying a current at lower voltage to follow up the high frequency current through the sparking plug gap and develop heat therein.

In one form of the invention the system includes an ignition coil or magneto, a high frequency circuit connected to the secondary winding of the coil through a trigger spark gap and coupled or connected to a sparking plug circuit so that the high frequency current resulting from a trigger gap spark will ionise the sparking plug gap, and means, independent of the secondary winding of the coil, for supplying to the sparking plug circuit a relatively low tension discharge following up the high frequency current to develop heat in the sparking plug gap.

The source of high tension impulses will generally be the ignition coil or magneto, the secondary winding of which is coupled or connected to the high frequency circuit, in which case the source of low tension current may be the primary winding of the ignition coil or magneto.

Conveniently, the high frequency circuit includes a high frequency transformer with its primary winding connected to the secondary winding of the ignition coil through a trigger spark gap, and its secondary winding arranged to be connected in series with the sparking plug across the primary circuit of the ignition coil. Alternatively, it may include a high frequency coil or auto-transformer connected to the secondary winding of the ignition coil through a trigger spark gap and arranged to be connected in series with a sparking plug across the contact breaker and condenser in the primary circuit of the ignition coil.

In this way it will be seen that the necessary low tension impulses to maintain the low tension spark discharge across the sparking plug gap, after its ionisation by the high frequency spark, will automatically be available at the time when each high frequency spark occurs.

Alternatively, however, in some cases, where for example it is desired to maintain the spark discharge across the sparking plug gap over a longer period, for the purpose say of igniting the fuel under adverse conditions, the low tension current may be supplied to the sparking plug circuit from a battery.

Where, as described above, the low tension current is supplied in the form of impulses from the primary winding of the magneto or ignition coil which also supplies the high tension impulses to the high frequency circuit, the primary winding of the magneto or ignition coil may be formed as an auto-transformer, the battery and contact breaker being connected across a portion of it whilst the sparking plug circuit is connected across the whole of it. A step-up effect is thereby obtained to increase the voltage of the low tension impulse supplied to the sparking plug circuit. Alternatively, or in addition, an inductance may be connected in series or in parallel with the primary winding of the ignition coil or magneto to increase the low tension energy available for discharge across the spark gap after ionisation by the high frequency spark. In a further alternative a similar effect is obtained by making the coupling between the primary and secondary winding of the ignition coil less than a maximum, for example by winding them on different limbs of a core having an air gap in it, to increase the energy avaiable from the primary circuit.

It will be understood that the invention can readily be applied to existing high frequency spark ignition systems wherein the secondary winding of the magneto or ignition coil is connected through a spark gap to the primary wind ing of a high frequency transformer by connecting the primary winding of the magneto or ignition coil to the end of the secondary Winding of the high frequency transformer which is not connected to the distributor or sparking plug, so as to deliver low tension impulses thereto from the primary winding of the magneto Or ignition coil. In such an arrangement, moreover, a se lector switch may be provided whereby the end of the secondary winding of the high frequency transformer not connected to the sparking plug or distributor can alternatively be connected to the primary winding of the magneto or ignition coil for starting purposes, or to earth for normal running when the engine is hot.

A peak voltage of the order of 250 volts normally occurs at the contact breaker of an ignition coil or magneto, and if the unearthed side of the contact breaker is connected to the secondary circuit of th high frequency transformer as described above, it will be seen that this voltage will discharge across the spark gap already ionised by the high frequency spark impulse and that in this way much of the excess energy, which is normally lost in heating the secondary winding of the ignition coil or magneto and in flashing across the contact breaker as it breaks, is usefully expended in the spark gap. Further only a small proportion of the voltage need be lost in traversing the secondary Winding of the high frequency transformer since the resistance of this secondary winding can be very low.

The invention may take various forms in prac tice but certain arrangements will be described purely by way of example with reference to the accompanying drawings in which Figures 1 to 5 are respectively circuit diagrams of five different arrangements.

In the form of the invention shown in Figure l as applied to a coil ignition system th apparatus comprises the usual coil A, the primary winding A of which is connected to a battery B through a switch B and the usual contact breaker C which is shunted by a condenser D. The secondary winding A of the coil is connected in series with a pilot spark gap E and the primary winding F of a high frequency transformer F and is shunted by a condenser G. The sparking plug H has one terminal connected to earth and the other terminal connected to one end of the secondary winding F of the high frequency transformer.

The arrangement so far described resembles known arrangements for high frequency coil ignition. In such known arrangements the other end of the secondary winding of the high frequency transformer would be connected to earth but in accordance with the invention this end of the secondary winding of the high frequency transformer is connected to the primary winding of the ignition coil. Hence, the circuit through the sparking plug and the secondary winding of the high frequency transformer is completed through the primary Thus, when the contact breaker opens, the sparking plug receives substantially simultaneously a high frequency impulse from the secondary winding of the high frequency transformer, which breaks down and ionises the spark gap, and a low tension impulse or surge from the primary winding of the ignition coil which diswinding of the ignition coil.

through this resistance but flows directly to the secondary winding of the high frequency transformer from the primary circuit, where a voltage builds up across the contact breaker. As normally constructed for radio purposes the resistance of this winding might be of the order or ohms. If, however, the maximum effectiveness of spark is required it is preferred to employ a high frequency coil or transformer of specially low resistance. This may be produced by winding a series of flat spirals of copper strip placed coaxiaiy so as to produce a suitable high frequency coil having a resistance of the order of a fifth of an ohm. Such a coil can be made relatively compact so as to require only a small screen.

The trigger gap may be of any preferred form but a cup gap in which one electrode is formed as a cup and the other is situated within it is generally preferred since it deionises more quickly. Such a gap may be mounted coaxially with the high frequency coil.

In one particular embodiment of the invention arranged as shown in Figure 3 the efiiciency of energy conversion was found to be of the order of 60 to 80 per cent, that is to say 60 to 80 per cent of the input energy was converted into heat in the sparking plug gap. As a result it was found that the ignition coil remained cold even with an input of some 70 watts.

It will be appreciated that the invention is not limited to the arrangements described by way of example or to the particular applications described. Thus, for example, it may be used for such purposes as starting an arc, whether between carbon or other solid electrodes or from a mercury electrode. It is, however, primarily applicable to the ignition of fuels and especially fuels that are difficult to ignite. For example, ordinary parafiin (kerosene) is accompanied by practically no vapour and in order to ignite it the spark must develop sufficient heat to vapourise it first.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electrical ignition system including an electrical impulse generator for producing high tension ignition current including a primary winding, a secondary winding, and a contact breaker; a source of high frequency energy including the said secondary Winding and an auxiliaryspark gap in series with it; a source of low tension energy including the said primar winding; and means for coupling a sparking plug circuit to the sources including low-pass impedance means in series with the said low tension source, so that the high frequency current resulting from an auxiliary gap spark will ionise the sparking plug gap, and a relatively low-tension discharge will follow it up to develop heat in the sparking plug gap.

2. An electrical ignition system including an electrical impulse generator for producing high tension ignition current including a primary winding, a secondary winding, and a contact breaker; a source of high frequency energy including the said secondary winding and an auxiliary spark gap in series with it; a source of low tension energy including the said primary Winding; and means for coupling a sparking plug circuit to the said sources including low-pass impedance means comprising high-frequenc transforming means in series with the said low tension source, so that the high-frequency current resulting from an auxiliary gap spark will ionise 8 the sparking plug gap, and a relatively low tension discharge will follow it up to develop heat in the sparking plug gap.

3. An electrical ignition system including an electrical impulse generator for producing high tension ignition current including a primary winding, a secondary winding, and a contact breaker; a source of high frequency energy including the said secondary Winding and an auxiliary spark gap in series with it; a source of low tension energy including the said primary winding; and means for coupling a sparking plug circuit to the said sources including low pass impedance means comprising a high-frequency transformer winding in series with the said low tension source, so that the high frequency current resulting from an auxiliary gap spark will ionise the sparking plug gap, and a relatively low tension discharge will follow it up to develop heat in the sparking plug gap.

4. An electrical ignition system including an electrical impulse generator for producing high tension ignition current including a primary winding, a secondary winding, and a contact breaker; a source of high freuqency energy including the said secondary winding and an auxiliary spark gap in Series with it; a source of low tension energy including the said primary winding; and means for coupling a sparking plug circuit to the said sources including low pass im-- pedance means comprising a high frequency auto-transformer winding in series with the said low tension source, so that the high frequency current resulting from an auxiliary gap spark will ionise the sparking plug gap, and a relatively low tension discharge will follow it up to develop heat in the sparking plug gap.

5. An electrical ignition system including an electrical impulse generator for producing high tension ignition current including a primary winding, a secondary winding, and a contact breaker; a source of high frequency energy including the said secondary winding and an aux- ,6. An electrical ignition system including an electrical impulse generator for producing high tension ignition current, a high frequenc transformer having a primary winding connected to said generator to the secondary winding of through an auxiliary spark ga and a secondary winding connected in series with the sparking plug circuit across the primary circuit of the said generator.

8. An electrical ignition system including an electrical impulse generator for producing high current, an auxiliary spark gap connected in series with the sparking plug circuit across the secondary winding of the said generator, and a high frequency choke connected in series with the sparking plug circuit across the primary circuit of the said generator.

9. An electrical ignition system including an electrical impulse generator for producing high tension ignition current, including a primary winding, a secondary winding, and a contact breaker; a source of high frequency energy including the said secondary winding and an auxiliary spark gap in series with it; a source of low tension energy including the said primary winding; means for coupling a sparking plug circuit to the said sources including low-pass impedance means in series with the said low tension source; and means for increasing the energy stored in the primary circuit.

10. An electrical ignition system including an ignition coil including a secondary winding, a, tapped primary winding constituting an autotransformer, and a contact breaker connected in circuit with a primary portion of said autotransformer; a source of high frequency energy including said secondary winding and an auxiliary spark gap in series with it; a source of low tension energy including the whole of said autotransformer winding; and means for coupling a. sparking plug circuit to said sources including low-pass impedance means in series with said low tension source.

11. An electrical ignition system including an ignition coil including a secondary winding, a tapped primary winding constituting an autotransformer, and a contact breaker connected in circuit with a primary portion of said auto-transformer; high frequency transforming means hav ing a primary winding connected to the secondary winding of the said ignition coil through an auxiliary spark gap, and a secondary winding connected in series with the sparking plug circuit across the whole of the primary winding of the said ignition coil.

12. An electrical ignition system including an electrical impulse generator for producing high tension ignition current, including a primary winding, a secondary winding, and a contact breaker; an inductance in series with said primary winding and contact breaker; a source of high-frequency energy including said secondary winding and an auxiliary spark gap in series with it; a source of low tension energy including said primary winding and said inductance; and means for coupling a sparking plug circuit to said sources including low-pass impedance means in series with said low tension source.

13. An electrical ignition system including an electrical impulse generator for producing high tension ignition current, including a primary winding, a secondary winding, and a contactbreaker; an inductance connected in series with the said primary winding and contact breaker, high frequency transforming means having a primary winding connected to the secondary Winding of the said generator through an auxiliary spark gap, and a secondary winding connected in series with the sparking plug circuit across the said inductance and the primary winding of the said generator.

14. An electrical ignition system including an electrical impulse generator for producing high tension ignition current, including a core with an air-gap in it, a primary winding and a secondary winding wound on separate limbs of the core to make the coupling between said windings less than a maximum, and a contact breaker; a source of high frequency energy including the said secondary winding and an auxiliary spark gap in series with it; a source of low tension energy including the said primary winding; and means for coupling a sparking plug circuit to the said sources including low-pass impedance means in series with the said low frequency source.

FRANK RAYMOND FABER RAMSAY.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date 2,409,202 Francis Oct.15, 1946 FOREIGN PATENTS Number Country Date 527,412 Great Britain Oct. 8, 1940 

